An inertial switch is a switch that can change its state, e.g., from open to closed, in response to acceleration and/or deceleration. For example, when the absolute value of acceleration along a particular direction exceeds a certain threshold value, the inertial switch changes its state, which change can then be used to trigger an electrical circuit controlled by the inertial switch. Inertial switches are employed in a wide variety of applications such as automobile airbag deployment systems, vibration alarm systems, detonators for artillery projectiles, and motion-activated light-flashing footwear.
A conventional inertial switch is a relatively complex, mechanical device assembled using several separately manufactured components such as screws, pins, balls, springs, and other elements machined with relatively tight tolerance. As such, conventional inertial switches are relatively large (e.g., several centimeters) in size and relatively expensive to manufacture and assemble. In addition, conventional inertial switches are often prone to mechanical failure.
One acceleration switch is manufactured using a layered wafer and has a movable electrode supported on a substrate layer of the wafer and a stationary electrode attached to that substrate layer. The movable electrode is adapted to move with respect to the substrate layer in response to an inertial force such that, when the inertial force per unit mass reaches or exceeds a contact threshold value, the movable electrode is brought into contact with the stationary electrode, thereby changing the state of the inertial switch from open to closed. The MEMS device is a substantially planar device, designed such that, when the inertial force is parallel to the device plane, the displacement amplitude of the movable electrode from a zero-force position is substantially the same for all force directions.
There is a need for a low-G MEMS acceleration switch. There is a further need for a MEMS acceleration switch that is insensitive to transverse loads. There is a further need for a MEMS acceleration switch that does not have the current flow through the entire device and provides for lower resistance in the closed state.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent upon a reading of the specification and a study of the drawings.